The present invention relates to a synchronizing signal regenerator for receiving a composite signal having a video signal and pulse code modulated audio multiplex signal arranged in a predetermined sequence and a plurality of pulse code modulated synchronizing signals being inserted in a predetermined position of said video signal and audio multiplex signal and required for the reproduction of said video signal and audio multiplex signal, and for reproducing signals each synchronizing with said plurality of synchronizing signals included in said composite signal.
A preferred embodiment of such a composite signal is a still picture broadcasting signal. Accordingly, the synchronizing signal regenerator according to the present invention is particularly suitable for use in a still picture broadcasting signal receiver.
The still picture broadcasting system has been disclosed in application Ser. No. 361,581 filed on May 18, 1973, now U.S. Pat. No. 3,854,010.
At first a brief explanation of said system will be given below.
In a still picture broadcasting signal transmission system, the video signal and the audio signal are transmitted alternately in a predetermined sequence. In one system of the still picture broadcasting signal, a video signal of 1/30 second duration and audio signal of 1/15 second duration are transmitted alternately. The video signal is transmitted at each horizontal scanning period of 1/f.sub.H (.apprxeq. 63.5 .mu.S) which is the same as a standard television braodcasting signal in a video signal transmission period. One video signal transmitted in one period of 1/30 sec represents one still picture, and therefore, at each video signal transmission period, one particular still picture content may be transmitted. In the audio signal transmission period, the audio signal is sampled at a repetition period of 1/f.sub.A which is different from that of the video signal. The audio signal is pulse code modulated and a number of such audio signals are multiplexed by a time division multiplex system and transmitted at said sampling period 1/f.sub.A. The synchronizing signals required for the reproduction of the video signal and audio signal are transmitted at each 1/f.sub.H period during the transmission of the video signal and 1/ f.sub.A period during the transmission of the audio signal. Besides the above-mentioned two synchronizing signals having two different repetition periods, various synchronizing signals are required having a different repetition period. The synchronizing signals which include such a kind of synchronizing signals mentioned above are constituted from pulse code modulated signals. More exactly, the synchronizing signals are formed by a blanking period, PCM frame pattern signal (referred to as PFP signal) for detecting the position of the synchronizing signal and having a predetermined pattern of pulses having the same bit timing with a modulated pulse series of the audio multiplex signal, and a mode control signal (referred to as MCC signal) formed of a horizontal synchronizing signal, audio PCM frame signal, video frame synchronizing signal, etc.
In the still picture broadcasting signal, the repetition period 1/f.sub.H of the synchronizing signal transmitted in the video signal transmission period and the repetition period 1/f.sub.A of the synchronizing signal transmitted in the audio signal transmission period are selected to be in a simple integral ratio relationship. Also the bit period t.sub.b of the pulse series forming the PFP signal and forming the modulated pulse series of the audio multiplex signal is so chosen to be in an integral ratio with said period of 1/f.sub.H and of 1/fA.
In order to receive the abovementioned still picture broadcasting signal and to display a selected picture on a picture display device and to reproduce a transmitted audio signal corresponding to said picture, it is necessary to detect the pulse code modulated synchronizing signal comprising the PFP signal and the MCC signal and to regenerate synchronizing signals for a respective period. The synchronizing signals formed by the PFP signal and the MCC signal are inserted in respective video and audio signals at their peak level substantially the same as that of the video and audio signals. Accordingly, the conventional means for separating the synchronizing signal from a standard television signal, such as for instance, an amplitude separating circuit using a slice circuit cannot be used for the detection of the synchronizing signal of the aforementioned still picture broadcasting signal. For the detection and reproduction of the synchronizing signal, a synchronizing signal regenerator having a particular synchronizing signal detector circuit is required.
For the detection and reproduction of a number of synchronizing signals, a corresponding number of detector circuits and a corresponding number of synchronizing signal regenerators are required.